Image: Discovery of a Dark Auroral Oval on Saturn

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ABOUT THIS IMAGE:

The ultraviolet image was obtained by the NASA/ESA Hubble Space
Telescope with the European Faint Object Camera (FOC) on June 1992.
It represents the sunlight reflected by the planet in the near UV
(220 nm).

The image reveals a dark oval encircling the north magnetic pole of
Saturn. This auroral oval is the first ever observed for Saturn, and
its darkness is unique in the solar system (L. Ben-Jaffel, V. Leers,
B. Sandel, Science, Vol. 269, p. 951, August 18, 1995). The
structure represents an excess of absorption of the sunlight at 220
nm by atmospheric particles that are the product of the auroral
activity itself. The large tilt of the northern pole of Saturn at
the time of observation, and the almost perfect symmetry of the
planet's magnetic field, made this observation unique as even the
far side of the dark oval across the pole is visible!

Auroral activity is usually characterized by light emitted around
the poles. The dark oval observed for Saturn is a STUNNING VISUAL
PROOF that transport of energy and charged particles from the
magnetosphere to the atmosphere of the planet at high latitudes
induces an auroral activity that not only produces auroral LIGHT but
also UV-DARK material near the poles: auroral electrons are probably
initiating hydrocarbon polymer formation in these regions.